There is an IC card that can function both as a contact IC card and a contactless IC card. When the IC card is used as a contact IC card, it uses a power supply voltage supplied from an external voltage supply via a contact power supply terminal. When the IC card is used as a contactless IC card, it uses a power supply voltage generated from an electromagnetic wave received at an antenna. Either one of a power supply voltage is supplied to a circuit mounted in the IC card via an internal power supply line.
According to a technology (e.g., see patent document 1: Japanese Patent Laid-open No. 2000-113148), such dual-purpose IC card uses a power supply switch circuit between a contact power supply terminal and an internal power supply line. When the IC card operates on a power supply generated from an electromagnetic wave received at an antenna, the IC card turns off an input from a contact power supply terminal.
According to another technology (e.g., see patent document 2: Japanese Patent Laid-open No. 2004-78898), a power supply switch circuit includes two serially connected PMOS transistors when the IC card is used as a contactless one. This aims at ensuring removal of the power from a contact power supply terminal of an internal power supply line. Serially connecting two PMOS transistors prevents generation of an electric current path due to a parasitic diode generated between bulk and source terminals of the PMOS transistor. This ensures removal of the power. Further, patent document 2 describes that a transistor for the power supply switch circuit is sized 700 times larger than a logical transistor in terms of an area ratio so as to reduce that transistor's on-resistance.